In these studies the relationship between genes controlling the immune response and structural genes which code for antibody synthesis will be investigated. It has been observed that rabbits heterozygous for certain L chain allotypes (b4, b9) preferentially select allotype b4 in synthesis of antibodies directed against streptococcal carbohydrates. Several experimental approaches are being used to determine the basis of this allelic selection. The relative binding affinities of b4 and b9 antibodies for the streptococcal antigens are being compared to ascertain whether there are differences that may influence the selection of antigens. These comparisons utilize elution profiles from immunoabsorbents to which streptococcal carbohydrates have been bound. Structural studies indicating that b4 and b9 light chains variable regions have amino acid sequence differences near the amino terminals suggest different V gene repertoires are associated with allotypically different L chains. Complete sequence analysis of b4 and b9 light chains will be carried out to ascertain whether significant differences exist in other areas of their variable regions. Streptococcal antibodies will be raised in rabbits heterozygous for other group b allotypes and their allotype ratios measured to determine whether allelic selection occurs among other combinations of allotypes.